1. Field of Invention
The present invention relates generally to methods and apparatus for use in monitoring the application of adhesive to finger joints and other wood surfaces, such as edge-glued surfaces and I-beams.
2. Background
In industries which use wood, e.g., the construction industry and the furniture-making industry, the practice of joining smaller pieces of wood together to create larger pieces of wood has long been employed. Smaller pieces of wood may be joined or bonded together to form a large piece of wood which may then be used for any suitable purpose, as for example, to create a table surface. Alternatively, pieces of wood which would otherwise be difficult to use because they are of a relatively small size may be joined together to form a larger piece of wood.
In order for the smaller pieces, or blocks, of wood to be joined together, the ends of the blocks are often cut to form "fingers," or interlocking structures. Although these fingers may take any suitable form, the fingers are generally formed as pointed extensions on the end of a block of wood that are arranged to interlock with fingers formed on the end of another block of wood. FIG. 1a is a diagrammatic representation of the ends of two beams, or blocks of wood, which may be assembled to form an end jointed beam. In general, end jointed beams are created from "scrap," e.g., small, pieces of lumber which might otherwise be discarded. However, as previously mentioned, end jointed beams may also be created from smaller pieces of lumber simply because a larger piece of lumber is desired.
A first beam 104 includes fingers 108 which are cut into the end of first block 104. It should be appreciated that first block 104 may be a board. A second block 112, like first block 104, includes fingers 116 that are cut into the end of second block 112. As shown, first block 104 includes seven fingers 108, and second block 112 includes seven fingers 116. It should be appreciated, however, that the number of fingers may be widely varied and is, in general, dependent at least in part upon the size of the block. Fingers 108 and fingers 116 are arranged to interlock such that first block 104 and second block 112 may together form a single overall beam, block, or board.
In order for blocks 104 and 112 to be securely fitted together, adhesive is generally applied on fingers 108 and/or fingers 116. It should be appreciated that adhesive may be applied on both the top surfaces 110 of fingers 108 and the bottom surfaces of the fingers. Alternatively, it may be possible for adhesive to be applied on just one surface of fingers, i.e., either top surfaces of fingers or bottom surfaces of fingers. By way of example, adhesive may be applied to top surfaces 110 of fingers 108 such that a bond is formed between fingers 108 and fingers 116 when fingers 108 and fingers 116 are interlocked. FIG. 1b is a diagrammatic representation of first block 104 with an adhesive coating 120 applied on the top surfaces of fingers 108. As shown, adhesive coating 120 substantially covers the top surfaces of fingers 108, i.e., adhesive coating 120 covers the top surfaces of fingers substantially between tips 119 and roots 121.
Adhesive application systems which are used to deposit adhesive on the surfaces of fingers of blocks, e.g., surfaces 110 of fingers 108, generally involve spreading a coating of adhesive on the surfaces. Although any suitable system may be used to deposit adhesive on fingers, two particularly suitable systems are described in U.S. Pat. Nos. 3,938,367 and 4,220,114, which are incorporated herein by reference in their entirety.
In general, adhesive application systems have been shown to be effective in forming coatings of adhesive on surfaces of fingers. However, the coatings of adhesive on surfaces of fingers may be uneven. In other words, there are instances when adhesive is not successfully applied to predefined locations. By way of example, air bubbles in adhesive may create voids in adhesive coatings. Alternatively, when an adhesive application system either malfunctions or exhausts an available supply of adhesive, the coating of adhesive on the surface of a finger may be uneven, or, in some cases, nonexistent.
As shown in FIG. 1c, an adhesive coating 122 on the top surface of a finger 108 of block 104 may include a void 124, or a section which is intended to be covered with adhesive but is left without adhesive. Void 124 may occur for any number of reasons, as for example when air bubbles are present in adhesive when adhesive coating 122 is formed, as mentioned above.
When a surface for a finger which is intended to be covered with adhesive is not properly covered with adhesive, the overall block created when fingers of two or more blocks are interlocked and "glued" together is considered to be imperfect. In other words, the bond between the pieces which make up the overall, or end-jointed, block, however strong the bond may be, is often considered to be marred. Such an end-jointed beam is generally considered to be a imperfect because of a void in the adhesive layer.
It should be appreciated that when smaller beams with fingers that are improperly coated with adhesive are joined together, the resulting end-jointed block may fail a quality inspection process. Typically, the quality inspection process is performed visually. Although visual inspection often works well, it is time consuming, relatively expensive and highly dependent upon the abilities of the inspector. Therefore, what is desired is an efficient method and apparatus for determining whether adhesive coatings are properly formed on the fingers that are to be used in a finger joint.